Optical fiber ribbons having a non-uniform thickness and/or preferential tear portions

ABSTRACT

A fiber optic ribbon includes a plurality of optical fibers arranged in a generally planar configuration having a primary matrix generally contacting optical fibers along a longitudinal axis forming an elongate structure. In one embodiment, the primary matrix has a cross-section with a non-uniform thickness, for example, an end portion with a generally bulbous shape. The fiber optic ribbon is useful as a subunit having a secondary matrix in contact therewith. The secondary matrix has a non-uniform thickness, thereby providing a fiber optic ribbon with preferential tear portions to aid separation of the ribbon into subunits. Other embodiments include a fiber optic ribbon with subunits having a secondary matrix with recessed portions to aid in the separation of the subunits.

FIELD OF THE INVENTION

The present invention relates generally to fiber optic ribbons. Morespecifically, the invention relates to fiber optic ribbons havingnon-uniform shapes and/or preferential tear portions for separating thefiber optic ribbon into subunits.

BACKGROUND OF THE INVENTION

Fiber optic ribbons include optical waveguides such as optical fibersthat transmit optical signals, for example, voice, video, and/or datainformation. Fiber optic cables using optical fiber ribbons can resultin a relatively high optical fiber-density. Fiber optic ribbonconfigurations can be generally classified into two general categories.Namely, fiber optic ribbons with subunits and those without. A fiberoptic ribbon with a subunit configuration, for example, includes atleast one optical fiber surrounded by a primary matrix forming a firstsubunit, and a second subunit having a similar construction, which arecontacted and/or encapsulated by a secondary matrix. On the other hand,fiber optic ribbons without subunits generally have a plurality ofoptical fibers surrounded by a single matrix material.

Optical fiber ribbons should not be confused with micro-cables that, forexample, have a strength member and a jacket. For instance, U.S. Pat.No. 5,673,352 discloses a micro-cable having a core structure and ajacket. The core structure requires that at least one optical fiber ispositioned between longitudinally extending strength members, both ofwhich are embedded in a buffer material. The jacket protects the corestructure and the material is selected to have good adhesion to thebuffer material and be abrasion resistant. Additionally, the strengthmembers are required to have a larger diameter than the diameter of theoptical fiber, thereby absorbing crushing forces that are applied to thecable.

On the other hand, optical fiber ribbons generally have a plurality ofadjacent optical fibers arranged in a generally planar array forming arelatively high optical fiber density. Optical fiber ribbons withoutsubunits can present problems for the craft. For example, whenseparating these optical fiber ribbons into optical fiber subsets, thecraft must use expensive precision tools. Moreover,connectorization/splice procedures can require inventories ofspecialized splice and closure units/tools for the various subsets ofoptical fibers. Where the craft elects to separate the optical fiberribbon into subsets by hand, or with a tool lacking adequate precision,stray optical fibers and/or damage to the optical fibers can result.Stray optical fibers can cause problems in optical ribbonconnectorization, organization, stripping, and splicing. Additionally,damage to the optical fibers is undesirable and can render the opticalfiber inoperable for its intended purpose.

However, there are fiber optic ribbon configurations that attempt to aidthe separation of fiber optic ribbons without using subunits. Forexample, U.S. Pat. No. 5,982,968 requires an optical fiber ribbon ofuniform thickness having V-shaped stress concentrations in the matrixmaterial that extend along the longitudinal axis of the fiber opticribbon. V-shaped stress concentrations can be located across from eachother on the planar surfaces of the fiber optic ribbon, thereby aidingthe separation of the fiber optic ribbon into subsets. However, the '968patent requires a wider fiber optic ribbon because additional matrixmaterial is required adjacent to the optical fibers near the V-shapedstress concentrations to avoid stray optical fibers after separation. Awider ribbon requires more matrix material and decreases the opticalfiber density. Another embodiment of the patent requires applying a thinlayer of a first matrix material around optical fibers to improvegeometry control such as planarity of the optical fibers. Then V-shapedstress concentrations are formed in a second matrix applied over thefirst matrix material, thereby allowing separation of the subsets at thestress concentrations.

Another example of a separable fiber optic ribbon is described in U.S.Pat. No. 5,970,196. More specifically, the '196 patent requires a pairof removable sections positioned in V-shaped notches located across fromeach other on opposite sides of the planar surfaces of an optical fiberribbon. The removable sections are positioned between adjacent interioroptical fibers of the optical fiber ribbon to facilitate the separationof the optical fiber ribbon into subsets at the V-shaped notches. Theremovable sections can either be flush with the planar surfaces of theoptical fiber ribbon, or they may protrude therefrom. These known fiberoptic ribbons have several disadvantages. For example, they can be moreexpensive and difficult to manufacture. Additionally, from anoperability standpoint, the V-shaped stress concentrations and/orV-shaped notches can undesirably affect the robustness of the opticalfiber ribbon and/or induce microbending in the optical fibers.

Fiber optic ribbons that employ subunits to aid separation generally donot encounter these problems; however, they can have other problems. Aconventional optical fiber ribbon 1 employing subunits encapsulated in asecondary matrix is shown in FIG. 1. Optical fiber ribbons havingsubunits can have several advantages, for example, improved separation,and avoidance of stray fiber occurrences. In particular, optical fiberribbon 1 includes a pair of conventional subunits 2 having opticalfibers 3 encapsulated in a primary matrix 5, which are then encapsulatedin a secondary matrix 4. The thickness T1 of primary matrix 5 iscontinuous and uniform. Likewise, the thickness t1 of the secondarymatrix 4 covering the planar portions of subunits 2 is continuous anduniform. For example, subunit 2 can include six 250 μm optical fibers 3disposed in primary matrix 5 having an overall uniform thickness T1 of310 μm and secondary matrix 4 has a thickness t1 of 10 μm for an overallfiber optic ribbon thickness T2 of 330 μm.

However, conventional optical fiber ribbon 1 has disadvantages. Forexample, one concern is the potential formation of wings W (FIG. 1)during hand separation of subunits 2. Wings W can be cause by, forexample, a lack of sufficient adhesion between common matrix 4 andsubunit matrix 5 and/or random fracturing of the secondary matrix duringseparation. The existence of wings W can negatively affect, for example,optical ribbon organization, connectorization, stripping, and/orsplicing operations by the craft. Additionally, wings W can causeproblems with ribbon identification markings, or compatibility of thesubunit with ribbon handling tools, for example, thermal strippers,splice chucks, and fusion splicers.

SUMMARY OF THE INVENTION

The present invention is directed to a fiber optic ribbon including aplurality of optical fibers arranged in a generally planar configurationwith a primary matrix. The primary matrix generally contacts andinhibits relative movement between the plurality of optical fibers alonga longitudinal axis forming an elongate structure. The primary matrixhas a cross-section with a non-uniform thickness having a first endportion and a medial portion. The first end portion having a generallybulbous shape having a thickness, and the medial portion has athickness, the thickness of the first end portion being greater than thethickness of the medial portion.

The present invention is further directed to a fiber optic ribbonincluding a first subunit, a second subunit, and a secondary matrix. Thefirst subunit includes a plurality of optical fibers being surrounded bya first primary matrix having a non-uniform thickness. The secondsubunit includes a plurality of optical fibers being surrounded by asecond primary matrix. The secondary matrix contacts portions of thefirst and second subunits and is dimensioned so as to provide a pair ofopposing generally flat planar surfaces. The secondary matrix has alocal minimum thickness adjacent to the non-uniform thickness of thefirst subunit, wherein during separation of the subunits the secondarymatrix fractures adjacent to the local minimum thickness.

The present invention is also directed to a fiber optic ribbon includinga first subunit, a second subunit, and a secondary matrix. The firstsubunit includes a first plurality of optical fibers being contacted bya first primary matrix having a first end portion. The second subunitincludes a second plurality of optical fibers being contacted by asecond primary matrix having a first end portion. The first and secondsubunits being generally aligned along a plane having a secondary matrixcontacting portions of the first and second subunits. The secondarymatrix has a cross-section with a non-uniform thickness and a recessedportion. The recessed portion being adjacent to an interface between thefirst end portion of the first subunit and the first end portion of thesecond subunit. The recessed portion defining a preferential tearportion.

The present invention is still further directed to a fiber optic ribbonincluding a plurality of optical fibers being arranged in a generallyplanar configuration having a primary matrix generally contacting andinhibiting relative movement between the plurality of optical fibersalong a longitudinal axis. The primary matrix having a first endportion, a second end portion, and a medial portion with a cross-sectionwith a non-uniform thickness. The thickness of the first end portionbeing greater than the thickness of the medial portion.

The present invention is also directed to a fiber optic ribbon includinga first subunit, a second subunit, and a secondary matrix. The firstsubunit includes a plurality of optical fibers being surrounded by afirst primary matrix. The second subunit includes a plurality of opticalfibers being surrounded by a second primary matrix. The secondary matrixcontacting portions of the first and second subunits and has at leastone generally planar surface. An interface is defined between the firstend portion of the first subunit and the first end portion of the secondsubunit. The interface having an interface axis that is generallyperpendicular to the generally planar surface of the secondary matrixand passes through the interface. The secondary matrix has at least tworecessed portions being on opposite sides of the interface axis.

Additionally, the present invention is directed to a fiber optic ribbonincluding a first subunit, a second subunit, and a secondary matrix. Thefirst subunit includes a plurality of optical fibers, the plurality ofoptical fibers being surrounded by a first primary matrix. The secondsubunit includes a plurality of optical fibers being surrounded by asecond primary matrix. The secondary matrix contacts portions of thefirst and second subunits and has at least one generally planar surface.An interface is defined between the first end portion of the firstsubunit and the first end portion of the second subunit. An interfaceaxis passes through the interface and is generally perpendicular to thegenerally planar surface of the secondary matrix. The secondary matrixhaving at least one recessed portion being generally symmetrical aboutthe interface axis.

BRIEF DESCRIPTION OF THE FIGS.

FIG. 1 is a cross-sectional view of a conventional optical fiber ribbonaccording to the background of the present invention.

FIG. 2 is a cross-sectional view of a fiber optic ribbon according toone embodiment of the present invention.

FIG. 3 is a cross-sectional view of another fiber optic ribbon accordingto the present invention.

FIG. 4 is a cross-sectional view of the fiber optic ribbon subunit ofFIG. 2 having a secondary matrix on portions thereof.

FIG. 5 is a cross-sectional view of another fiber optic ribbon accordingto the present invention.

FIG. 6 is a cross-sectional view of the fiber optic ribbon of FIG. 5after separation into subunits.

FIG. 7 is a cross-sectional view of another fiber optic ribbon accordingto the present invention.

FIG. 8 is a cross-sectional view of another fiber optic ribbon accordingto the present invention.

FIG. 9 is a cross-sectional view of another fiber optic ribbon accordingto the present invention.

FIG. 10 is a schematic, partial cross-sectional view of another fiberoptic ribbon according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in FIG. 2 is a fiber optic ribbon 10 according to thepresent invention. Fiber optic ribbon 10 (hereinafter ribbon) includes aplurality of optical waveguides, for example, optical fibers 12 arrangedin a generally planar configuration with a primary matrix 14 forming anelongate structure. Ribbon 10 can, for example, be used as a stand-aloneribbon, a portion of a ribbon stack, or as a subunit of a ribbon.Primary matrix 14 generally contacts optical fibers 12 and mayencapsulate the same, thereby providing a robust structure forprocessing and handling. Primary matrix 14 generally fixes adjacentoptical fibers together in an elongate structure, thereby inhibitingrelative movement therebetween. Primary matrix 14 includes a first end14 a, a medial portion 14 b, and a second end 14 c. Additionally,primary matrix 14 has a cross-section having a non-uniform thickness.

In this embodiment, first end portion 14 a has a thickness T_(a) andsecond end portion 14 c has a thickness T_(c), which are both greaterthan a thickness T_(b) of medial portion 14 b. For example, thicknessT_(a) is about 5 μm or greater than thickness T_(b); however, othersuitable dimensions can be used. More particularly, first and second endportions 14 a,14 c both have a generally bulbous shape; however, othersuitable shapes can be used such as angular or elliptical. As usedherein, bulbous shape means that an end portion of the ribbon has athickness that is greater than the largest thickness of a medial portionof the ribbon. Preferably, the largest thickness is generally adjacentto edge fiber 12 a, generally at a range r of about one-half to aboutone optical fiber diameter from the edge of the matrix, however, othersuitable ranges can be used.

The present invention should not be confused with conventional ribbonshaving undulations across their cross-sections surfaces due tomanufacturing variances. These undulations can cause variations in theconventional ribbon thickness at random locations, rather than, forexample, predetermined shapes. For example, the thickness of theconventional ribbon can be 310±3 μm at random locations across thecross-section. On the other hand, ribbons according to the presentinvention can have, for example, a non-uniform thickness that increasesor decreases at predetermined locations to aid separation performance.

In one embodiment, optical fibers 12 are a plurality of single-modeoptical fibers; however, other types or configurations of optical fiberscan be used. For example, optical fibers 12 can be multi-mode,pure-mode, erbium doped, polarization-maintaining fiber, other suitabletypes of light waveguides, and/or combinations thereof. For instance,each optical fiber 12 can include a silica-based core that is operativeto transmit light and is surrounded by a silica-based cladding having alower index of refraction than the core. Additionally, one or morecoatings can be applied to optical fiber 12. For example, a soft primarycoating surrounds the cladding, and a relatively rigid secondary coatingsurrounds the primary coating. The coating can also include anidentifying means such as ink or other suitable indicia foridentification and/or an anti-adhesion agent that inhibits the removalof the identifying means. However, optical fibers used in ribbons of thepresent invention generally are not tight-buffered. Suitable opticalfibers are commercially available from Corning Incorporated of Corning,N.Y.

Primary matrix 14 can be, for example, a radiation curable material or apolymeric material; however, other suitable materials can be used. Asknown to one skilled in the art, radiation curable materials undergo atransition from a liquid to a solid when irradiated with predeterminedradiation wavelengths. Before curing, the radiation curable materialincludes a mixture of formulations of, for example, liquid monomers,oligomer “backbones” with acrylate functional groups, photoinitiators,and other additives. Typical photoinitiators function by: absorbingenergy radiated by the radiation source; fragmenting into reactivespecies; and then initiating a polymerization/hardening reaction of themonomers and oligomers. Generally, as a result of irradiation, a curedsolid network of cross-linking is formed between the monomers andoligomers, which may include fugitive components. Stated another way,the photoinitiator begins a chemical reaction that promotes thesolidification of the liquid matrix into a generally solid film havingmodulus characteristics.

One aspect of the curing process is the reaction of a photoinitiator inresponse to radiation exposure. A photoinitiator has an inherentabsorption spectrum that is measured in terms of absorbance as afunction of radiation wavelength. Each photoinitiator has acharacteristic photoactive region, i.e., a photoactive wavelength rangetypically measured in nanometers (nm). For example, commerciallyavailable photoinitiators can have a photoactive wavelength range in thevacuum ultra-violet (160-220 nm), ultra-violet (220-400 nm), or visiblelight (400-700 nm) wavelength ranges.

The resulting modulus of radiation curable materials can be controlledby factors such as radiation intensity and cure time. The radiationdose, i.e., the radiant energy arriving at a surface per unit area isinversely proportional to the line speed, i.e., the speed the radiationcurable moves past the radiation source. The light dose is the integralof radiated power as a function of time. In other words, all else beingequal, the faster the line speed, the higher the radiation intensitymust be to achieve adequate curing. After a radiation curable materialhas been fully irradiated, the material is said to be cured. Curingoccurs in the radiation curable material from the side facing theradiation source down or away from the source. Because portions of thematerial closer to the radiation source can block radiation fromreaching non-cured portions of the material, a cure gradient can beestablished. Depending on the amount of incident radiation, a curedmaterial may exhibit different degrees of curing. Moreover, the degreesof curing in a material can have distinct modulus characteristicassociated therewith. Conversely, radiation sources can be positioned sothat the material has a relatively uniform cure.

Thus, the degree of cure affects the mechanical characteristics throughthe cross-link density of the radiation curable material. For example, asignificantly cured material can be defined as one with a highcross-link density for that material, which is, for example, toobrittle. Further, an undercured material may be defined as one having alow cross-link density, and can be too soft, possibly having arelatively high coefficient of friction (COF) that causes an undesirablelevel of ribbon friction. The cured UV material has a modulus, forexample, in the range of about 50 MPa to about 1500 MPa depending on theradiation dose. Different modulus values can provide varying degrees ofperformance with respect to, for example, hand separability androbustness of the ribbons of the present invention.

In one embodiment, a UV curable material is used for primary matrix 14.For example, the UV curable material is a polyurethane acrylate resincommercially available from DSM Desotech Inc. of Elgin Ill. such as950-706. Alternatively, other suitable UV materials can be used, forexample, polyester acrylate resin commercially available from BordenChemical, Inc. of Columbus, Ohio. Additionally, thermoplastic materialssuch as polypropylene can be used as a matrix material.

FIG. 3 illustrates a ribbon 20 another embodiment of the presentinvention that is similar to ribbon 10. Ribbon 20 includes a pluralityof optical waveguides, for example, optical fibers 12 arranged in agenerally planar configuration with a primary matrix 24 forming anelongate structure. Primary matrix 24 generally contacts optical fibers12 and may encapsulate the same, thereby providing a robust structurefor processing and handling. Primary matrix 24 includes a cross-sectionhaving a non-uniform thickness having a first end 24 a, a medial portion24 b, and a second end 24 c. In this embodiment, first end portion 24 ahas a thickness T_(a) and second end portion 24 c has a thickness T_(c),wherein thickness T_(a) is greater than a thickness T_(b) of medialportion 24 b. More particularly, first end portion 24 a, for example,has a generally bulbous shape; however, other suitable shapes can beused. Whereas, second end portion 24 c can have a shape that isgenerally different than the shape of first end portion 24 a. Forexample, as depicted, second end portion 24 c has a generally roundshape, however, other suitable shapes can be used such as flat orangled. When stacking a plurality of ribbons similar to ribbon 20, firstend portion 24 a can be placed on alternating sides of the ribbon stackto provide stack integrity. Additionally, stacking ribbons in thismanner still allows the ribbons to move in at least two degrees offreedom when acted upon by forces, which can preserve opticalperformance.

FIG. 4 depicts a ribbon 40. Ribbon 40 includes ribbon 10 with asecondary matrix 45 disposed on outwardly portions of primary matrix 14.Using more than one can have several advantages. For example, in oneembodiment a thin primary matrix can be applied to ensure planarity ofthe optical fibers in the ribbon. Additionally, secondary matrix 45 canhave several functions. For example, secondary matrix 45 can be usedimpart generally planar surfaces 46 to ribbon 40. Planar surfaces 46 canalso provide stability when ribbon 40 is used as a portion of a ribbonstack. Additionally, secondary matrix 45 may also provide materialcharacteristics that are different from primary matrix 14 such asadhesion, COF characteristics, or hardness. This can be accomplished,for example, by using a secondary matrix 45 material that is similar toprimary matrix 14 with different processing characteristics such as curecharacteristics, or by using a material that is different than primarymatrix 14. Likewise, different portions of secondary matrix 45 can bedifferent materials and/or have distinct material characteristics.

Illustratively, a first planar surface of secondary matrix 45 can have apredetermined COF, while the second planar surface can have a highadhesion to primary matrix 14. A predetermined COF on the planar surfaceallows the ribbon to relieve strain, for example, during bending of astack of ribbons. While a high adhesion characteristic between theprimary and secondary matrices can make for a generally robust ribbon.In other embodiments, the first and second planar surfaces can have thesame characteristics, which may differ from the characteristics of theprimary matrix. Additionally, as disclosed in U.S. Pat. No. 6,253,013,which is incorporated in its entirety herein by reference, an adhesionzone 44 (FIG. 4) can be used between primary matrix 14 and secondarymatrix 45. For example, adhesion zone 44 is applied to primary matrix 14using a Corona discharge treatment. Additionally, a marking indicia foridentifying ribbon 40 can be printed either on primary matrix 14 orsecondary matrix 45. In other embodiments, secondary matrix 45 can beused to identify ribbon 40. For example, secondary matrix 45 can becolored with a dye for identification of the ribbon.

Likewise, other suitable color combinations are possible for identifyingindividual ribbons. In one embodiment, primary matrix 14 may be a firstcolor and secondary matrix 45 a second color. For example, multipleribbons of a ribbon stack can have the same color primary matrix witheach different ribbon have a secondary matrix with a different color.Thus, the craftsman could identify the stack as the blue stack and eachindividual ribbon within the blue stack. In other embodiments, thesecondary matrix of the ribbons of the stack can be the same color, withthe primary matrix of the individual ribbon having different colors.Thus, each ribbon can be identified from the side of the stack. In stillother embodiments, the primary or secondary matrix can have stripes, ortracers, of suitable colors for use as identifying indicia.

FIG. 5 depicts ribbon 50 another embodiment according to the presentinvention. Ribbon 50 includes two ribbons such as ribbons 10 for use asa first subunit 51 and a second subunit 52. As used herein, subunitmeans a plurality of optical fibers having a discrete matrix materialthereon. In other words, each subunit has its own individual matrixmaterial thereon. Subunits should not be confused with subsets, whichare optical fibers arranged as groups having a common matrix material.When subunits are separated the discrete matrix material generallyremains intact on each subunit. However, ribbons according to thepresent invention can use other suitable types or numbers of ribbons assubunits.

A secondary matrix 55 contacts portions of subunits 51,52 and isgenerally dimensioned to provide a pair of opposing generally flatplanar surfaces 56. Secondary matrix 55 can have materialcharacteristics that are similar or different than primary matrix. Forexample, the primary matrix around the edge fibers of subunits 51,52 canbe relatively soft to cushion the same and inhibit optical attenuationtherein. The generally flat planar surfaces 56 allow ribbon 50 to beeasily stacked to form a portion of a ribbon stack. However, othersuitable shapes of secondary matrix 55 can be used. Using secondarymatrix 55 allows separation of ribbon 50 at the interface 57 between thesubunits 51,52 by, for example, hand. Subunits 51,52 preferably have apoint contact at interface 57, thereby allowing secondary matrix 55 toflow between the subunits and forming a robust structure.

Additionally, ribbon 50 advantageously inhibits the formation of, forexample, wings and/or stray optical fibers during separation. Ribbon 50inhibits the formation of wings by having a preferential tear portion 58in secondary matrix 55, rather than allowing random fracturing insecondary matrix 55. Specifically, preferential tear portion 58 isgenerally located at a point of local minimum thickness t2 (FIG. 6)generally adjacent to interface 57 of secondary matrix. In this case,the local minimum thickness t2 is formed by subunits 51,52 havingnon-uniform cross-sections. When secondary matrix 55 with generally flatplanar surfaces 56 is applied over these non-uniform cross-sections, thethickness of secondary matrix 55 varies. For example, local minimumthickness t2 is about 2 μm, whereas portions of the secondary matrix 55over the medial portions of subunits 51,52 have a thickness of about 10μm. In other embodiments, local minimum thickness t2 can approach avalue of essentially zero. Local minimum thickness t2 is a weak point,thereby allowing the fracture of secondary matrix 55 to begin and/orterminate at this point. Additionally, the minimum thickness can haveother suitable dimensions or locations, but should allow the ribbon tohave a suitable robustness and handleability. FIG. 6 illustrates theribbon 50 after separation by hand into subunits. As depicted, formationof wings is inhibited according to the concepts of the presentinvention. Additionally, using suitable matrix characteristics such aselongation to break and/or a predetermined matrix modulus can enhancethe preferential tear portion.

As depicted in FIG. 7, preferential tear portion can be accomplishedwith other suitable ribbon geometries. Ribbon 70 includes two subunits71,72 and a secondary matrix 75. Secondary matrix 75 contacts and/orencapsulates subunits 71,72 thereby forming ribbon 70. Like secondarymatrix 55 of ribbon 50, secondary matrix 75 has a thickness that variesgenerally adjacent to interface 77 between subunits 71,72. However, thevarying thickness of secondary matrix 75 adjacent interface 77 isaccomplished with subunits 71,72 having a generally uniform thickness.However, this ribbon configuration can be used in combination withsubunits having a non-uniform thickness. In one embodiment, secondarymatrix 75 has a recessed portion having a width w, for example, therecessed portion defining a concave portion 73 generally centered overinterface 77. In other words, recessed portions are generallysymmetrical about an interface axis A—A that passes through interface 77and is generally perpendicular to the generally planar surfaces ofribbon 70. However, in other embodiments, the recessed portion can haveother shapes such as indentation 74, widths, and/or locations. Forpurposes of illustration, the top and bottom of ribbon 70 have differentconfigurations of the recessed portion; however, embodiments can havethe same shaped recessed portions 73 on each side of interface 77.Concave portions 73 form a local minimum thickness in secondary matrix75, which is a weak point that advantageously allows the fracture ofsecondary matrix 75 to begin and/or terminate at this point during, forexample, hand separation.

In one embodiment, recessed portion 73 has a width w less than about 600μm and a depth D of about 5 μm. However, other suitable dimensions canbe used, for example, in other embodiments width w can be about 200 μmor greater and depth D can be about 5 μm or greater. Furthermore, therecessed portions 73 of the ribbon should be dimensioned to providesuitable robustness and handleability for the intended application ofthe ribbon.

Ribbon 80, another embodiment according to the concepts of the presentinvention, is illustrated in FIG. 8. Ribbon 80 includes a pair ofsubunits 81,82, each having a generally uniform thickness, and asecondary matrix 85 generally contacting and/or encapsulating subunits81,82, thereby forming ribbon 80. Ribbon 80 has at least one recessedportion 83 and is similar to ribbon 70; however, recessed portions 83are centered over an interface 87 between subunits 81,82. In thisembodiment, recessed portions 83 have a generally concave shape that isoffset at a distance d from interface 87. For example, distance d isbetween about 125 μm and about 300 μm, but other suitable distances canbe used. Additionally, recessed portions 83 can have other shapes,widths, and/or depths. For purposes of illustration, the top and bottomof ribbon 80 have a different number of recessed portions 83. Forexample, recessed portions 83 on the top of ribbon 80 are generallysymmetrical about interface axis A—A. However, other embodiments canhave the same, or different, number of recessed portions 83 on eachgenerally planar surface 86, for example, one, two, or more. Concaveportions 83 form a local minimum thickness in secondary matrix 85, whichis a weak point that advantageously allows the fracture of secondarymatrix 75 to begin and/or terminate at this point during, for example,hand separation, thereby inhibiting the formation of wings.

Recessed portions 83 should be dimensioned to provide suitablerobustness and handleability for the intended application of the ribbon.In this embodiment, centering recessed portions 83 of ribbon 80 atdistance d from interface 87 provides increased robustness to ribbon 80.Specifically, centering recessed portions 83 from interface 87 improvesthe twist performance of ribbon 80. For example, subunits 81,82 ofribbon 80 are less likely to separate during normal handling of theribbon.

FIG. 9 illustrates a ribbon 90 that is another embodiment of the presentinvention that is similar to ribbon 50. Ribbon 90 includes subunits91,92 and a secondary matrix 95. Secondary matrix 95 contacts and/orencapsulates subunits 91,92 thereby forming ribbon 90. Subunits 91,92have a non-uniform thickness and secondary matrix 95 has a plurality ofrecessed portions, like ribbon 70. In this embodiment, recessed portions83 are on both sides of interface axis A—A and are generally symmetricalthereabout. The recessed portions are defined as a plurality of concaveportions 93; however, recessed portions can have other shapes, widths,and/or locations. Concave portions 93 are generally located at adistance d from the interface of subunits 91,92. In this embodiment,distance d locates the center of concave portions 93 slightly beyond thelargest thickness of the ends towards the medial portions of thesubunits 91,92.

FIG. 10 illustrates a portion of ribbon 100, which is another embodimentthat is similar to ribbon 90. Ribbon 100 includes subunits 101,102 and asecondary matrix 105. Subunits 101,102 have a non-uniform thickness andsecondary matrix 105 has plurality of recessed portions that aresymmetrical about interface axis A—A, thereby forming a local minimumthickness t2. In this embodiment, local minimum thickness t2 is formedby having a radius R₁ of the subunit being less than an adjacent radiusR₂ of the primary matrix, thereby forming a preferential tear portion.For example, local minimum thickness t2 can have a range of about zeroto about 5 μm; however, any other suitable dimension can be used. RadiiR₁ and R₂ are generally located adjacent to local minimum thickness t2.Configuring the ribbon so that R₂ is greater than R₁, is intended toallow primary matrix 105 material to generally flow away from localminimum thickness t2 before curing or hardening of the same. Rather thanhave primary matrix material flow towards, and building-up the thicknessof local minimum thickness t2 before curing or hardening of the same.Additionally, other embodiments can also use this concept.

Many modifications and other embodiments of the present invention,within the scope of the appended claims, will become apparent to askilled artisan. For example, subunits can include different numbers ofoptical fibers, ribbons can have more than two subunits, or the ribbonscan have other suitable configurations. Additionally, ribbons of thepresent invention can be part of a ribbon stack or include othersuitable components. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosedherein and that modifications and other embodiments may be made withinthe scope of the appended claims. Although specific terms are employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation. The invention has been described withreference to silica-based optical fibers, but the inventive concepts ofthe present invention are applicable to other suitable opticalwaveguides as well.

That which is claimed:
 1. A fiber optic ribbon comprising: a pluralityof optical fibers, the plurality of optical fibers being arranged in agenerally planar configuration; and a primary matrix, the primary matrixgenerally contacts and inhibits relative movement between the pluralityof optical fibers along a longitudinal axis forming an elongatestructure, the primary matrix having a first end portion and a medialportion, the primary matrix having non-uniform thickness, wherein thefirst end portion has a generally bulbous shape that is at leastpartially disposed over an edge optical fiber, the generally bulbousshape having a thickness, and the medial portion has a thickness, thethickness of the first end portion being greater than the thickness ofthe medial portion.
 2. The fiber optic ribbon according to claim 1, theprimary matrix further includes a second end portion having a thickness,the thickness of the second end portion being greater than the thicknessof the medial portion.
 3. The fiber optic ribbon according to claim 1the thickness of the first end portion being about 5 μm or greater thanthickness of the medial, portion.
 4. The fiber optic ribbon according toclaim 2, further comprising a secondary matrix contacting a portion ofthe primary matrix, the secondary matrix having a minimum thicknessadjacent to the first end portion.
 5. The fiber optic ribbon accordingto claim 1, the fiber optic ribbon being a first subunit, the firstsubunit being generally aligned along a plane with a second subunit, thefirst and second subunits having respective portions thereof contactinga secondary matrix.
 6. The fiber optic ribbon according to claim 5, thesecond subunit a non-uniform thickness.
 7. The fiber optic ribbonaccording to claim 1, further comprising a secondary matrix having apredetermined modulus contacting a portion of the primary matrix, theprimary matrix having a predetermined modulus, and the modulus of thesecondary matrix being different than the modulus of the primary matrix.8. The fiber optic ribbon according to claim 1, further comprising asecondary matrix having at least one predetermined materialcharacteristic contacting a portion of the primary matrix, the primarymatrix having at least one predetermined material characteristic, andthe at least one predetermined material characteristic of the secondarymatrix being different than the at least one predetermined materialcharacteristic of the primary matrix.
 9. The fiber optic ribbonaccording to claim 1, the fiber optic ribbon being a subunit having asecondary matrix in contact therewith, the secondary matrix having alocal minimum thickness, the subunit having a radius adjacent to thelocal minimum thickness, and the secondary matrix having a radiusadjacent to the local minimum thickness, wherein the radius of thesubunit is smaller than the radius of the secondary matrix.
 10. Thefiber optic ribbon according to claim 9, the local minimum being in therange of about zero to about 5 μm.
 11. The fiber optic ribbon accordingto claim 1, a majority of the first end portion being disposed over anedge optical fiber.
 12. The fiber optic ribbon according to claim 1,further comprising a secondary matrix that forms at least one generallyplanar surface.
 13. A fiber optic ribbon comprising: a first subunit,the first subunit including a plurality of optical fibers, the pluralityof optical fibers being connected by a first primary matrix, the firstprimary matrix having a non-uniform thickness that is generally thickernear a first end portion; a second subunit, the second subunit includinga plurality of optical fibers, the plurality of optical fibers beingconnected by a second primary matrix; and a secondary matrix contactingportions of the first and second subunits, the secondary matrix beingdimensioned so as to provide a pair of opposing generally flat planarsurfaces, the secondary matrix having a local minimum thickness adjacentto the non-uniform thickness of the first subunit, wherein duringseparation of the subunits the secondary matrix fractures adjacent tothe local minimum thickness.
 14. The fiber optic ribbon according toclaim 13, second primary matrix having a non-uniform thickness.
 15. Thefiber optic ribbon according to claim 13, the first end portion of thefirst subunit having a generally bulbous shape.
 16. The fiber opticribbon according to claim 13, the first subunit having a second end, thefirst and second ends having generally bulbous shapes.
 17. The fiberoptic ribbon according to claim 13, the first subunit further includesmedial portion and a second end, the first end has a predeterminedthickness, the medial portion having a predetermined thickness, and thesecond end having a predetermined thickness, the thickness of the firstand second ends being greater than the thickness of the medial portion.18. The fiber optic ribbon according to claim 13, the secondary matrixhaving at least one predetermined material characteristics, and thefirst primary matrix having at least one predetermined materialcharacteristic, wherein the at least one predetermined materialcharacteristic of the secondary matrix is different than the at leastone predetermined material characteristic of the first primary matrix.19. The fiber optic ribbon according to claim 13, the first subunithaving a radius adjacent to the local minimum thickness, and thesecondary matrix having a radius adjacent to the local minimumthickness, wherein the radius of the subunit is smaller than the radiusof the secondary matrix.
 20. The fiber optic ribbon according to claim19, the local minimum thickness being in the range of about zero toabout 5 μm.
 21. A fiber optic ribbon comprising: a first subunit, thefirst subunit including a first plurality of optical fibers, the firstplurality of optical fibers being contacted by a first primary matrixhaving a non-uniform thickness that is generally thicker near a firstend portion; a second subunit, the second subunit including a secondplurality of optical fibers, the second plurality of optical fibersbeing contacted by a second primary matrix, the second primary matrixhaving a first end portion; the first and second subunits beinggenerally aligned along a plane; a secondary matrix contacting portionsof the first and second subunits, the secondary matrix having anon-uniform thickness; and the secondary matrix having a recessedportion, the recessed portion being adjacent to an interface between thefirst end portion of the first subunit and the first end portion of thesecond subunit, the recessed portion defining a preferential tearportion.
 22. The fiber optic ribbon according to claim 21, the recessedportion having a width of about 200 μm or greater.
 23. The fiber opticribbon according to claim 21, the recessed portion having a width thatis less than about 600 μm.
 24. The fiber optic ribbon according to claim21, the first end portion of the first subunit having a generallybulbous shape.
 25. The fiber optic ribbon according to claim 21, thefirst subunit further comprising a medial portion, the medial portionhaving a thickness, and the first end portion of the first subunithaving a thickness, the thickness of the first and portion of the firstsubunit being greater than the thickness of the medial portion.
 26. Thefiber optic ribbon according to claim 25, the thickness of the first endportion being about 5 μm or greater than thickness of the medialportion.
 27. The fiber optic ribbon according to claim 25, the firstsubunit having a radius adjacent to a local minimum thickness of thesecondary matrix, and the secondary matrix having a radius adjacent tothe local minimum thickness, wherein the radius of the subunit issmaller than the radius of the secondary matrix.
 28. The fiber opticribbon according to claim 21, the second subunit having a non-uniformthickness.
 29. The fiber optic ribbon according to claim 21, the firstend portion of the first subunit having a bulbous shape and the firstend portion of the second subunit having a bulbous shape.
 30. The fiberoptic ribbon according to claim 21, the second subunit having generallyuniform thickness.
 31. The fiber optic ribbon according to claim 21, therecessed portion being generally centered over the interface.
 32. Thefiber optic ribbon according to claim 21, the recessed portion beinggenerally offset from the interface.
 33. The fiber optic ribbonaccording to claim 32, the offset being in the range of about 125 μm toabout 300 μm.
 34. The fiber optic ribbon according to claim 21, thesecondary matrix having at least one predetermined materialcharacteristic, and the primary matrix of the first subunit having atleast one predetermined material characteristic, wherein the at leastone predetermined material characteristic of the secondary matrix isdifferent than the at least one predetermined material characteristic ofthe primary matrix.
 35. A fiber optic ribbon comprising: a plurality ofoptical fibers, the plurality of optical fibers being arranged in agenerally planar configuration; and a primary matrix, the primary matrixhaving a first end portion, a second end portion, and a medial portion,the primary matrix generally contacts and inhibits relative movementbetween the plurality of optical fibers along a longitudinal axis, theprimary matrix has a non-uniform thickness, wherein the first endportion has a thickness and the medial portion has a thickness, thethickness of the first end portion being greater than the thickness ofthe medial portion, and the first end portion is at least partiallydisposed about an edge optical fiber.
 36. The fiber optic ribbonaccording to claim 35, a majority of the first end portion beingdisposed about an edge optical fiber.
 37. The fiber optic ribbonaccording to claim 35, further comprising a secondary matrix that formsat least one generally planar surface.
 38. A fiber optic ribboncomprising: a first subunit, the first subunit including a plurality ofoptical fibers, the plurality of optical fibers being surrounded by afirst primary matrix; a second subunit, the second subunit including aplurality of optical fibers, the plurality of optical fibers beingsurrounded by a second primary matrix; a secondary matrix contactingportions of the first and second subunits, the secondary matrix havingat least one generally planar surface; an interface, the interface,being defined between the first end portion of the first subunit and thefirst end portion of the second subunit; an interface axis, theinterface axis generally passes through the interface and is generallyperpendicular to the generally planar surface of the secondary matrix;and at least two recessed portions disposed within the secondary matrix,the at least two recessed portions being on opposite sides of theinterface axis.
 39. The fiber optic ribbon according to claim 38, the atleast two recessed portion being generally symmetrical about theinterface axis.
 40. A fiber optic ribbon comprising: a first subunit,the first subunit including a plurality of optical fibers, the pluralityof optical fibers being surrounded by a first primary matrix, the firstprimary matrix having non-uniform thickness that is generally thickernear a first end portion; a second subunit, the second subunit includinga plurality of optical fibers, the plurality of optical fibers beingsurrounded by a second primary matrix; a secondary matrix contactingportions of the first and second subunits, the secondary matrix havingat least one generally planar surface; an interface, the interface beingdefined between the first end portion of the first subunit and the firstend portion of the second subunit; an interface axis, the interface axisgenerally passes through the interface and is generally perpendicular tothe generally planar surface of the secondary matrix; and at least onerecessed portion disposed within the secondary matrix, the at least onerecessed portions being generally symmetrical about the interface axis.